Hepatitis A is a worldwide distributive acute disease caused by infection with hepatitis A virus (HAV) which is a picornavirus closely related to the poliovirus. Infection is spread by the fecal/oral route and consequently the disease in endemic in areas where hygiene and sanitation standards are lower. Recent reports on epidemical survey show that in developing countries including China, there are as many as 4 million hepatitis A cases per year. There is frequently large-scale outbreak and rapid spread in certain regions with poor social and economic status, especially after various disasters. In these countries or regions, as the high incidence of hepatitis A, some serious public health and social problems have been encountered. On the other hand, in the United States and other developed countries, hepatitis A accounting for approximately 150,000 cases, that is approximately 25% of all clinical hepatitis cases.
Therefore, to successfully immunize against hepatitis A in developing countries as well as in developed countries, it is necessary to vaccinate the entire people, especially entire pediatric populations. So there will be an increasing need for hepatitis A vaccine.
An effective vaccine would be useful for active immunization of populations at high risk. Generally, there are four types of vaccines used for inducing a specific neutralizing antibody against challenge with virus or bacteria: live vaccine, inactivated vaccine, subunit vaccine (component vaccine), and recombinant vaccine. In these vaccines, the live attenuated vaccine could elicit a stronger protective response than others, and could have a significant impact on the eradication of the diseases.
U.S. Pat. Nos. 4,532,215 and 4,636,469 described, respectively a strain of wild-type HAV, designated HM-175, initially isolated from the faces of a patient, and adapted to passage in vitro in African green monkey kidney culture cell and methods for obtaining a vaccine by serial passaging. Also, CN Patent Nos. 89106580.6 and 92114998 disclose the preparation of attenuated HAV designated H2-and L-A-I, respectively.
With regard to live attenuated hepatitis A vaccine, it is worth mentioning the live HAV vaccine based on strain CR*326F (Merck & Co. Inc.), which is under preclinical trials, and the vaccines based on strain H2 and L-A-I, respectively, have been licensed for practical use and industrial-scale production in China. Clinical serological studies demonstrated that these live attenuated hepatitis A vaccines, especially the vaccine prepared from L-A-I strain of HAV (produced by Changchun Institute of Biological Products Ministry of Public Health, Changchun, China) evoked high titers of antibody response, in most volunteers receiving the vaccine, after only one dose and no systemic complains were present immediately after vaccination or during long-term follow-up (see CN Patent No. 92214998).
However, all of the live hepatitis A vaccines used so far are in the form of aqueous suspensions. One of the main disadvantages of live attenuated vaccine is having unsatisfactory theremo-stability, even in the situation of lyophilization at ambient temperature, hence it must be stored and transported in a frozen state and used soon after thawing to insure effective vaccination. Hepatitis A virus, as well as measles virus is unsatisfactory in both storage stability and heat resistance. For example, live attenuated hepatitis A virus survives only for about 7 days at a temperature of 2-8° C., and storage-term duration is only about 3-6 months. Therefore, transportation and storage of these vaccine preparations must be completed at a reduced temperature (e.g., −20° C. or lower), referred to as “cold chain.” As a direct result, the increases in production and transportation cost and user's expense are unavoidable, especially in developing countries and tropical and semitropical areas. This cost would be an obstacle to implementation of the worldwide Expanded Program on Immunization (EPI) founded by World Health Organization (WHO).
For the reasons as described above, eradication of hepatitis A will depend on the ability to provide hepatitis. A vaccine formulations having improved thermo-stability. Accordingly, there remains a distinct need in the art for live hepatitis vaccine formulations with enhanced storage stability and heat resistance during and after lyophilization.